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Selective Hydrogenation of Fatty Nitriles to Primary Fatty Amines: Catalyst Evaluation and Optimization Starting from Octanenitrile
Alessa Hinzmann and Harald Gröger*
In this contribution, an evaluation of the potential of various homogeneous and heterogeneous catalysts for a selective hydrogenation of fatty nitriles toward primary amines is reported exemplified for the conversion of octanenitrile into octane-1-amine as a model reaction. When using heterogeneous catalysts such as the ruthenium catalyst Ru/C, the palladium catalyst Pd/C, and the platinum catalyst Pt/Al2O3, low selectivities in the hydrogenation are observed, thus leading to a large portion of secondary and tertiary amine side-products. For example, when using Ru/C as a heterogeneous catalyst, high conversions of up to 99% are obtained but the selectivity remains low with a percentage of the primary amine being at 60% at the highest. The study further reveals a high potential of homogeneous ruthenium and manganese catalysts. When also taking into account economical considerations with respect to the metal price, in particular, manganese catalysts turn out to be attractive for the desired transformation and their application in the model reaction leads to the desired primary amine product with excellent conversion, selectivity, and high yield.
Practical Applications: This work describes an optimized hydrogenation process for transforming fatty nitriles to their corresponding primary amines. In general, fatty amines belong to the most applied fatty acid-derived compounds in the chemical industry with an annual product volume exceeding 800 000 tons per year in 2011 and are widely required in the chemical industry since such compounds are either directly used in home products such as fabric softeners, dishwashing liquids, car wash detergents, or carpet cleaners or in a broad range of industrial products, for example, lubricating additives, flotation agents, dispersants, emulsifiers, corrosion inhibitors, fungicides, and bactericides, showing additional major applications, e.g., in the detergents industry. Among them primary amines play an important industrial role. However, a major concern of current processes is the lack of selectivity and the formation of secondary and tertiary amines as side-products. By modifying a recently developed catalytic system based on manganese as economically attractive and environmentally benign metal component an efficient and selective access to fatty amines when starting from the corresponding nitriles is achieved. For example, hydrogenation of octanenitrile leads to a synthesis of octane-1-amine with>99% conversion and excellent selectivity with formation of secondary and tertiary amine side-products being suppressed to an amount of<1%.
1. Introduction
Fatty amines play an important role in the chemical industry since such compounds are either directly used in home prod- ucts such as fabric softeners, dishwashing liquids, car wash de- tergents, or carpet cleaners or in a broad range of industrial products, for example, lubricating additives, flotation agents, dispersants, emulsifiers, corrosion inhibitors, fungicides, and bactericides.[1–3] The worldwide demand of fatty amines was A. Hinzmann, Prof. H. Gröger
Chair of Industrial Organic Chemistry and Biotechnology Faculty of Chemistry
Bielefeld University
Universitätsstr. 25, 33615 Bielefeld, Germany E-mail: harald.groeger@uni-bielefeld.de DOI: 10.1002/ejlt.201900163
800 000 tons in 2011,[3]thus representing a further large-scale op- tion for the use of fats and oils as renewable building blocks and alternative raw material sources to petrochemicals. Among them, primary fatty amine are highly requested target products. When starting from fats and oils, today’s established large-scale applied route is based on the hydrogenation of fatty nitriles (Scheme 1).
Such fatty nitriles needed as substrates are today industrially manufactured via transformation of vegetable oils through their acids into fatty amides, followed by subsequent dehydration into their corresponding fatty nitriles under high temperatures of 280–360 °C and frequently in the presence of a metal oxide catalyst (Scheme 1).[1] As an alternative to this route via the amide intermediate (which shows disadvantages such as the required high reaction temperatures),[1]such fatty nitriles can be also prepared by a chemoenzymatic pathway starting from fatty aldehydes as further type of fatty acid derivatives (Scheme 1),[4–6]
Scheme 1. Overview about the overall industrial production concept for primary fatty amines.
Recently, we demonstrated such a process being suitable to be operated at high substrate loading of up to 1.4 kg L–1aqueous medium exemplified for octanenitrile.[5]
However, in spite of straightforward accesses to the fatty nitrile substrates and established hydrogenation technologies at large industrial scale, a hurdle that remained widely unsolved up to now in this field of fatty amines is the insufficient selectivity of the hydrogenation process (Scheme 1). Typically, with the currently applied heterogeneous metal catalysts the correspond- ing secondary and tertiary amines are also formed besides the desired primary amine products. For example, when using Pd/C as a heterogeneous catalyst (being frequently used for various types of hydrogenation reactions), the tertiary amine is formed as a major product in the hydrogenation of aliphatic nitriles.[7,8]
Also in case of the heterogeneous catalysts Ru/C[9] and Raney nickel,[10,11] insufficient selectivities toward the primary amine have been observed. Although some modifications of hydro- genation conditions and additives were found, which positively influence the selectivity of the Ni-catalyst for primary amines in the hydrogenation of nitriles, there is still a demand for general procedures to hydrogenate various nitriles and in particular aliphatic nitriles selectively to primary amines.[12,13]
A perspective to overcome these hurdles can be seen in the use of homogeneous in spite of the today’s applied heterogeneous catalysts. Due to the option to vary the ligand sphere, selectiv- ity can be fine-tuned, thus shifting the selectivity into direction of the desired primary amines. However, again there are some challenges to solve: often homogeneous catalysts for this purpose
are based on expensive heavy metals. Further issues to be solved are the tasks of high catalytic efficiently (and, thus, high turnover number) and bulk technically feasible strategies for separating and reusing the catalysts. Addressing the first two issues of using a low cost metal component being ideally environmental benign and achieving a high efficiency besides excellent selectivity, we became interested to explore manganese catalysts. Our interest in such catalysts was sparked by the recent achievements from the Kirchner group[14,15]who reported on hydrogenation of vari- ous nitriles using such manganese catalysts.
In the following, we report our results on the search of a suit- able catalyst providing both high efficiency as well as selectivity for the hydrogenation of fatty nitriles exemplified for octaneni- trile (Scheme 2). This study comprised an initial re-evaluation of various types of heterogeneous and homogeneous metal catalysts in terms of selectivity and a subsequent study and optimization of a manganese hydrogenation catalysts, which turned out to be promising for the desired reaction.
2. Results and Discussion
First, we defined a model reaction for our catalyst evaluation study and chose the hydrogenation of octanenitrile into octan-1- amine as representative reaction due to practical and analytical reasons. After having established a NMR-based -analytical method for the determination of the reaction course, we started with the screening of a range of heterogeneous catalysts as such
Scheme 2. Hydrogenation of octanenitrile as model reaction.
Table 1.Hydrogenation of octanenitrile (1) using the heterogeneous ruthenium catalyst Ru/C.
Catalyst T[°C] p[bar] t[h] Conversion [%] 2a/2b/2c
Ru/C (1 mol%) 27 14 20 – n.d.
Ru/C (1 mol%) 27 22 20 – n.d.
Ru/C (5 mol%) 27 13 20 – n.d.
Ru/C (5 mol%) 27 22 20 – n.d.
Ru/C (1 mol%) 27 1 19 – n.d.
Ru/C (5 mol%) 27 1 19 – n.d.
Ru/C (1 mol%) 100 10 20 72 45/53/2
Ru/C (1 mol%) 100 20 20 77 50/48/2
Ru/C (5 mol%) 100 10 20 71 45/54/1
Ru/C (5 mol%) 100 20 20 81 45/52/3
Ru/C (1 mol%) 80 1 19 – n.d.
Ru/C (5 mol%) 80 1 19 – n.d.
Ru/C (1 mol%)a) 100 20 20 99 60/37/3
a)Addition of 2 equivalents NH3to the hydrogenation reaction.
types of catalysts are today used in industry, thus representing the industrial benchmark. Furthermore, we were interested whether adjusting the reaction conditions to mild conditions would in principle enable a sufficient reactivity while achieving an im- provement in terms of selectivity. To start with the heterogeneous ruthenium catalyst Ru/C,[9,16]we varied the temperature broadly between 27 and 100 °C in addition to the hydrogen pressure, which was adjusted between 1 and 22 bar (Table 1). The reaction
time remains relatively constant at 19 or 20 h, respectively. It turned out that in general an elevated temperature of 100 °C is needed for this transformation, reaching conversions of 71%
to 99% in these cases. For the latter case, addition of ammonia (2 equivalents) was needed. In general, ammonia is added to hydrogenation reactions of nitriles in order to prevent the formation of secondary and tertiary amines,[9] since ammonia then serves as an alternative to the amine in the reaction with
Table 2.Hydrogenation of octanenitrile (1) using the heterogeneous palladium catalyst Pd/C.
Catalyst T[°C] p[bar] t[h] Conversion [%] 2a/2b/2c
Pd/C (10 mol%) 25 1 21 >99 0/96/4
Pd/C (10 mol%)a) 25 10 21 >99 5/77/18
Pd/C (10 mol%) 25 10 21 >99 0/81/19
Pd/C (10 mol%) 25 20 21 >99 0/89/11
Pd/C (10 mol%)a) 25 20 21 >99 5/82/13
Pd/C (1 mol%) 25 10 21 88 0/53/47
Pd/C (0.1 mol%) 25 10 21 65 0/65/35
Pd/C (0.05 mol%) 25 10 21 27 11/70/19
Pd/C (1 mol%) 25 1 21 >99 0/62/38
Pd/C (0.1 mol%) 25 1 21 <1 n.d.
Pd/C (1 mol%)a) 25 20 20 >99 4/45/51
a)Addition of 2 equivalents NH3to the hydrogenation reaction.
the imine intermediate. An elevated hydrogen pressure (20 bar in comparison to 10 bar) had a slightly positive impact on the conversion of nitriles, although the selectivity with respect to the formation of primary, secondary, or tertiary amines is not significantly influenced (Table 1). However, it is noteworthy that independent of the reaction conditions (and even when adding ammonia as a strategy to suppress formation of secondary and tertiary amines), the selectivity remained low with a percentage of the desired primary amine being at 60% at the highest. Thus, formation of secondary and tertiary amines remained as severe side-reactions having a significant impact in general when using Ru/C as a heterogeneous catalyst.
The formation of such side products are a result of the derivatization of the formed primary amine products, which are converted into imines and subsequently reduced to secondary amines.[16]An analogous derivatization of the secondary amine then gives the tertiary amine.
A further heterogeneous catalyst being commonly used for metal-catalyzed hydrogenation is Pd/C.[7,8,16–18]When operating under smooth reaction conditions such as 25 °C as reaction tem- perature and 1–20 bar hydrogen pressure, a minimum amount of 1 mol% of the catalyst Pd/C was found to be needed for achieving a high conversion within a reaction time of 20 or 21 h (Table 2). For example,>99% conversion was obtained at just 1 bar of hydrogen pressure and at a low reaction temperature of 25 °C. However, the amount of the desired primary fatty amine was very low with 0–4% under such conditions. Even when varying the catalyst loading between 0.05 and 10 mol%, the highest percentage of the primary amine product compared to the secondary and tertiary amine products was only 11%
(Table 2). Varying the hydrogen pressure and catalyst loading does not have a strong impact on the selectivity of the hydrogena- tion reaction. When using this catalyst, the major product was always found to be the secondary amine even when ammonia was added as an additive (the only exception is the reaction with 1 mol% Pd/C and 20 bar of hydrogen, which gave the tertiary amine as major product). However, as expected, the conversion of the nitrile drops with the decrease of the catalyst loading.
Besides ruthenium and palladium, platinum is a further metal component being frequently used for hydrogenation purpose.[19–21]When utilizing Pt/Al2O3as a catalyst at a catalytic loading of 1 mol%, a high conversion of up to 92% was achieved when operating at a hydrogen pressure of 20 bar and at a reaction temperature of 100 °C (Table 3). However, again the selectivity was limited and the percentage of the desired primary amine did not exceed 44%. In contrast to the hydrogenation experiments with the Ru/C catalyst, we could not find any or only a very low positive effect of the addition of ammonia on the selectivity of the hydrogenation when using Pd/C or Pt/Al2O3 as a catalyst.
While in case of Ru/C, the product ratio changed from 45/52/3 to 60/37/3, which shows that a significantly larger amount of primary amine was formed during the reaction in the presence of added ammonia, in case of Pt/Al2O3, the ratio did not im- prove in terms of formation of the primary amine, and in case of Pd/C only a slightly increased amount of primary amine was formed.
In general, these results are in accordance to those in litera- ture for the hydrogenation of nitriles to amines in the presence of heterogeneous catalysts.[7–13]For example, Sajiki et al. showed
Table 3.Hydrogenation of octanenitrile (1) using the heterogeneous platinum catalyst Pt/Al2O3.
Catalyst T[°C] p[bar] t[h] Conversion [%] 2a/2b/2c
Pt/Al2O31 mol%) 100 20 20 85 44/53/3
Pt/Al2O31 mol%)a) 100 20 20 92 41/56/3
a)Addition of 2 equivalents NH3to the hydrogenation reaction.
that utilizing Pd/C as heterogeneous catalyst at 25°C and H2 atmosphere for the hydrogenation of decanenitrile in methanol mainly leads to the secondary and tertiary amine.[7]This result is in principle in good agreement with our findings when using this catalyst in isopropanol for the hydrogenation of octanenitrile (Table 2). In our case, at atmospheric pressure of hydrogen at room temperature mainly the secondary amine was formed as a product. Compared to our study in literature often other nitrile substrates were used such as 3-methoxy propionitrile,[9]
benzonitrile,[18]decanenitrile,[7]or pentanenitrile,[8]which makes a direct comparison of conversions, yields, and selectivities dif- ficult. However, in particular in case of pentanenitrile[7] and decanenitrile,[8] which are structurally close to our model sub- strate octanenitrile, the results in literature[7,8] and from our study appear to be comparable.
Taking into account the low selectivities and high amount of unfavored side-products when using heterogeneous catalysts, we turned our interest to the evaluation of homogeneous catalysts for the model reaction. Homogeneous catalysis in our cases al- ways means that the catalyst is dissolved in the reaction mixture during the hydrogenation reaction. Furthermore, even after the hydrogenation reaction the reaction mixture was found to homo- geneous without precipitation of catalyst or additives. Based on the work of Beller et al. with ruthenium catalysts,[22] we applied various species for the hydrogenation of octanenitrile in different solvents (Table 4). The best results were obtained when using the commercial Ru-MACHO-BH catalyst[23]in isopropanol or alter- natively the Ru-Gusev catalyst,[24,25]which turned to be suitable in various solvents such as isopropanol, diisopropylethyer, and cyclohexane. In these hydrogenations, high conversions in the range of 81–99% were obtained at a catalyst loading of 0.5 mol%.
Furthermore, excellent selectivities were achieved in such hydro- genations with an amount of desired product of at least 98%. For example, when using the Takasago catalyst Ru-MACHO-BH,[18]
98% conversion and a product ratio of>99:0:0 were observed in our model reaction.
The increased selectivity of hydrogenation reactions for pri- mary amines when using a homogeneous catalyst in comparison to heterogeneous catalysts might be rationalized by the option of homogeneous catalysis to fine-tune the catalytic complex by
means of ligands, which, among other effects, then could result in a different catalytic activity for hydrogenating the various con- ceivable imine intermediates as precursors for the primary, sec- ondary, and tertiary amine products. In this connection, it should be added that a detailed calculation for the heterogeneous Pd- catalyzed hydrogenation of acetonitrile and the reaction steps to- ward the corresponding primary, secondary, and tertiary amines have been performed and discussed by Adamczyk.[26]
Next, we focused on the impact of catalyst loading which ap- pears to be even more crucial in homogeneous catalysis due to the more difficult catalyst recovery and re-use compared to heteroge- neous catalysis. However, when reducing the catalyst loading to 0.1 mol%, conversion drops significantly and did not exceed 18%
(Table 4). Thus, improving catalyst activity as well as stability and developing options for its re-use are a task for future research in this field. At the same time we were seeking for a more econom- ical alternative with respect to the metal component due to the high price of ruthenium being currently in the range of 8.150
$ kg–1.[27] An economically attractive alternative would be iron or manganese as center ion in homogeneous metal catalysts. In- spired by a successful manganese catalyst reported recently from the Kirchner group[14,15]for being suitable in hydrogenation of various functional groups including nitriles (leading to 93% yield for octanenitrile),[15]we focused on this type of catalysts also for our model reaction. Under slightly different reaction conditions and catalyst structure to those described in literature with a pro- longed reaction time from 18 to 19 h and using ethyl instead of n-propyl substituents at the phosphine ligand of the manganese complex for practical reasons, we achieved a high conversion of
>99% in the presence of 2 mol% of the manganese catalyst6
(Table 5). The reaction was conducted at 100 °C in toluene at a substrate concentration of 144 mm and a hydrogen pressure of 50 bar. After work-up, we obtained octan-1-amine in 68% yield, indicating a loss of product during downstream-processing. In order to further improve stability of this catalyst, we speculated if more rigid derivatives bearing cyclohexyl instead of ethyl sub- stituents also could represent active catalysts with potential for higher stability. Thus, we prepared the new catalyst7and to our delight this catalyst led to both, excellent conversion of>99% and yield of 96%.
Table 4.Hydrogenation of octanenitrile (1) using the homogeneous ruthenium catalysts 3–5.
Catalyst Solvent T [°C] p [bar] t [h] Conversion [%] 2a/2b/2c
3 iPrOH 70 20 3 98 >99/0/0
3a) iPrOH 70 20 3 18 >99/0/0
3 THF 70 20 3 12 >99/0/0
3 iPr2O 70 20 3 6 86/8/6
3 Cyclohexane 70 20 3 2 >99/0/0
4 iPrOH 70 50 3 99 98/2/2
4 THF 70 50 3 71 65/31/4
4 iPr2O 70 50 3 98 1/97/2
4 Cyclohexane 70 50 3 81 99/0/1
5 iPrOH 70 60 3 6 0/83/17
5 iPr2O 70 60 3 9 0/75/25
5 Cyclohexane 70 60 3 <1 0/0/100
a)In this experiment, 0.1 mol% catalyst loading was used instead of 0.5 mol% (which was the catalyst loading in case of all other experiments shown in Table 4)
Encouraged by these results, we further investigated the hy- drogenation of octanenitrile using the MnI-catalyst7focusing on reduction of the catalyst loading as a next step (Table 6). When reducing the catalyst loading from 2 mol%, which was used in the initial experiment, to 1, 0.5, and 0.1 mol%, we could ob- tain a quantitative conversion towards octane-1-amine without identifying secondary or tertiary amines as by-product in case of 1 mol%. By lowering the catalyst loading to 0.5 mol%, however, a decreased conversion of 51% toward the primary amine was found.
In addition, we investigated the impact of different solvents on this hydrogenation reaction. Besides toluene as solvent used in the initial experiments with the Mn-catalysts6and7, we tested tetrahydrofurane (THF), 2-methyl tetrahydrofurane (2-Me-THF), ethanol, and isopropanol (Table 6). When using a catalyst loading of 2 mol% of catalyst7,full conversion toward the primary amine
was reached in all cases without formation of by-products. How- ever, at a decreased catalyst loading of 1 mol% of catalyst7,only in case of toluene and 2-Me-THF a full conversion was obtained, while the use of ethanol, isopropanol, and THF led to lower con- versions.
After optimization of the hydrogenation conditions for the syn- thesis of octane-1-amine, we conducted a hydrogenation experi- ment under such optimized conditions using dodecanenitrile (8) as a substrate (Scheme 3).
When using this fatty nitrile8as a starting material and the manganese complex7as a catalyst at a catalytic loading of 1 mol%, also full conversion to the primary amine9awithout for- mation of secondary or tertiary amines was obtained. This exper- iment indicates that this hydrogenation method is applicable for the synthesis of various fatty primary amines of different chain- lengths starting from the corresponding aliphatic nitriles.
Table 5.Hydrogenation of octanenitrile (1) using the homogeneous manganese catalysts6and7.
Catalyst T [°C] p [bar] t [h] Conversion [%] Yield [%] 2a/2b/2c
6 100 50 19 >99 68 >99/0/0
7 100 50 19 >99 96 >99/0/0
Table 6.Hydrogenation ofn-octanenitrile (1) using the homogeneous manganese catalyst7—optimization experiments in terms of catalyst loading and solvent.
Catalyst loading t-BuOK loading Organic solvent T [°C] Conversion [%] 2a/2b/2c
2 mol%a) 20 mol% Toluene 100 >99 >99/0/0
1 mol% 10 mol% Toluene 100 >99 >99/0/0
0.5 mol% 5 mol% Toluene 100 51 51/0/0
0.1 mol% 1 mol% Toluene 100 <1 n.d.
2 mol% 20 mol% THF 100 >99 >99/0/0
2 mol% 20 mol% 2-Me-THF 100 >99 >99/0/0
2 mol% 20 mol% Ethanol 100 >99 >99/0/0
2 mol% 20 mol% Isopropanol 100 >99 >99/0/0
1 mol% 10 mol% THF 100 71 >99/0/0
1 mol% 10 mol% 2-Me-THF 100 >99 >99/0/0
1 mol% 10 mol% Ethanol 100 53 >99/0/0
1 mol% 10 mol% Isopropanol 100 58 >99/0/0
a)This experiment is also shown in Table 5.
Scheme 3. Hydrogenation of dodecanenitrile using Mn-catalyst7.
3. Conclusions
In conclusion, an evaluation of the potential of various homoge- neous and heterogeneous catalysts for a selective hydrogenation of fatty nitriles toward primary amines was done exemplified for the conversion of octanenitrile into octan-1-amine as a model reaction. When using heterogeneous catalysts, low selectivities were observed, thus leading to a large portion of secondary and tertiary amine side-products. The study further revealed a high potential of homogeneous ruthenium and manganese catalysts.
When also taking into account economical considerations with respect to the metal price, in particular manganese catalysts turned out to be attractive for the desired transformation and their application in the model reaction led to the desired primary amine product with excellent conversion and selectivity and in high yield.
4. Experimental Section
Hydrogenation reactions were performed in a Parr Series 5000 Multi- ple Reactor System in which up to six different hydrogenations were con- ducted in parallel. The maximum volume of the used autoclaves was 75 mL and the reaction mixtures were stirred at 1000 rpm. In case of hetero- geneous catalysts, a Teflon inlet was used to prevent adsorption of the catalyst to the stainless-steel autoclave material. Before usage of the reac- tors, they were evaporated and filled with Argon twice. Afterward the nitrile (250 mm in all cases except for hydrogenations using MnI-catalysts6and 7) and solvent (10 mL total volume) were added in an Argon counter flow.
Finally, the catalyst and potentially used additives were added under in- ert conditions. In case of hetereogeneous catalysts sometimes ammonia was used as an additive. Ammonia (2 eq based on nitrile concentration) was added by adding ammonia in methanol (7 M) to the reaction mix- ture. Manganese catalysts6and7were used in combination witht-BuOK (10x catalyst concentration, e.g. 10 mol%t-BuOK when 1 mol%6or7 was used) as additive. The autoclaves were placed into the Parr Series
5000 Multiple Reactor System, which among others consists of a burst protection for high pressure reactions. The reactors were washed with ni- trogen (3×≈20 bar) to prevent formation of oxyhydrogen gas formation and afterward with hydrogen (2×≈20 bar, 1×required pressure) before adjusting the hydrogen-pressure to required pressure in every reactor. Af- ter stirring for the desired reaction time, the autoclaves were washed with nitrogen (3×≈20 bar) before cooling to room temperature and work-up.
Heterogeneous catalysts were filtered and homogeneous catalysts were removed by filtration over a≈2 cm celite (Celite 545, Merck) layer. The filter cake or celite layer was washed with solvent (same as used in hydro- genation experiment) twice (each≈5 mL). The solvent was removed in vacuo and the product was analyzed by1H-NMR spectroscopy and ESI–
MS. NMR spectra were recorded on a Bruker Avance III 500 at a frequency of 500 MHz (1H) or 125 MHz (13C). Chemical shift𝛿was given in ppm and referenced to the corresponding solvent signal (CDCl3). Nano-ESI mass spectra were recorded using an Esquire 3000 ion trap mass spectrome- ter (Bruker Daltonik GmbH, Bremen, Germany) equipped with a nano-ESI source. Samples were dissolved in methanol or acetonitrile and introduced by static nano-ESI using in-house pulled glass emitters. Nitrogen served both as nebulizer gas and dry gas. Nitrogen was generated by a Bruker ni- trogen generator NGM 11. Helium served as cooling gas for the ion trap and collision gas for MSnexperiments. The mass axis was externally cali- brated with ESI-L Tuning Mix (Agilent Technologies, Santa Clara, CA, USA) as calibration standard.
Octan-1-amine (2a):1H-NMR (500 MHz, CDCl3)𝛿/ppm=2.66 (t, 2H, NH2-CH2-(CH2)6-CH3), 1.42-1.29 (m, 12H, NH2-CH2-(CH2)6-CH3), 0.86 (t, 3H, -CH3).
ESI-MS (positive ions) [C8H19N+H]+m/z(calc.)=130.15,m/z(exp.)
=130.10.
Dodecan-1-amine (9a):1H-NMR (500 MHz, CDCl3)𝛿/ppm=2.69 (t, 2H, NH2-CH2-(CH2)6-CH3), 1.43-1.25 (m, 20H, NH2-CH2-(CH2)6-CH3), 0.87 (t, 3H, -CH3).
ESI-MS (positive ions) [C12H27N+H]+m/z(calc.)=186.21,m/z(exp.)
=186.12.
Abbreviation
equiv, equivalents
Supporting Information
Supporting Information is available from the Wiley Online Library or from the author.
Acknowledgements
The authors gratefully acknowledge generous support from the Fachagen- tur Nachwachsende Rohstoffe (FNR) and the German Federal Ministry of Food and Agriculture (BMEL), respectively, within the funding programme on the utilization of biorenewables (grant number: 22001716).
Conflict of Interest
The authors declare no conflict of interest.
Keywords
fatty amines, fatty nitriles, hydrogenation, manganese catalysts, primary amines
Received: August 22, 2019 Revised: September 30, 2019
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